GB1574225A - Quantitative analysis of aluminium/carbon and aluminium/hydrogen bonds - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 574 225 ( 21) Application No 22484/77 ( 22) Filed 27 May 1977 ( 31) Convention Application No.

2624204 ( 32) Filed 29 May 1976 in ( 33) Federal Republic of Germany (DE) ( 44) ( 1 Complete Specification Published 3 September 1980 ( 51) INT CL 3 GO O N 31/16 ( 52) Index at Acceptance G 1 B BA \ ( 54) IMPROVEMENT IN AND RELATING TO THE QUANTITATIVE ANALYSIS OF ALUMINIUM/CARBON AND ALUMINIUM/HYDROGEN BONDS ( 71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 02, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:

The invention relates to the quantitative analysis of aluminium/carbon and aluminium/ hydrogen bonds present in organic compounds.

There are several industrially interesting processes in which organoaluminium compounds are used as catalysts or as co-catalysts, for example the low pressure polymerisation of a-olefins according to the methods of Ziegler and Natta, in which the organoaluminium compounds are usually present in relatively low concentrations (< 10 mmoles/dm 3) The quantitative analysis of organoaluminium compounds in this concentration range is of considerable interest.

Methods for the quantitative analysis of organoaluminium compounds are described in the literature (see T R Compton, Analysis of Organoaluminium and Organozinc compounds, Pergamon Press 1968, and H Lehmkul, K Ziegler in Houben-Weyl, Methoden der Organischen Chemie 13/4, 291, ( 1970)).

Generally the methods described can only be applied at relatively high concentrations, and none of these methods can be used in the concentration range of < 10 mmoles/dm 3.

However, this is the concentration range used in, for example, the low pressure polymerisation of a-olefins.

We have now found that "active" aluminium present in hydrocarbons can be analysed quantitatively even in the concentration range of < 10 mmoles/dm 3, if the aluminium compound is decomposed with an alcohol and the unreacted alcohol is subjected to back titration with a coloured organometallic compound.

The invention provides a process for the quantitative analysis of aluminium/carbon and aluminium/hydrogen bonds in a sample comprising one or more hydrocarbons and con 50 taining at least one compound having an aluminium/carbon and/or aluminium/hydrogen bond, which comprises reacting the sample with an excess of an alcohol and backtitrating the unreacted alcohol and/or any 55 compound, or compounds, formed during the reaction which contain acidic hydrogen atoms with a solution of a coloured organometallic compound, which compound is the reaction product of an alkali metal with a polynuclear 60 aromatic hydrocarbon, wherein the coloured organometallic compound is decolourised by reaction with all the acidic hydrogen atoms present.

Preferably the alcohol is an alkanol, and is 65 especially a lower alcohol The term "lower" when used herein with reference to an alcohol refers to an alcohol having from 1 to 6 carbon atoms.

Preferably the aluminium/carbon and/or 70 aluminium/hydrogen bonds are present in the substrate in a concentration of less than m moles/dm 3.

It is possible to analyse substrates which also contain aluminium/halogen and/or 75 aluminium/alkoxy bonds as although these bonds react with the alcohol when they do so acidic hydrogen atoms are produced which are able to be detected together with the unreacted alcohol, as described hereinafter 80 The coloured organometallic compound should be one which will react with acidic hydrogen atoms, and may be used in solution.

The solvent for the coloured organometallic compound may be, for example, a polar 85 organic solvent used in the preparation of the organometallic compound itself.

According to the process of the invention, the organoaluminium compound is quantitatively decomposed with an excess of an 90 1 574 225 alcohol, preferably a lower alcohol, for example methanol, ethanol, isopropanol, n-propanol, or a butanol, preferably methanol, at room temperature, or, if necessary, at a higher temperature The temperature for the decomposition may be, for example, from 10 to C, preferably from 20 to 70 C The Al-C and Al-H bonds are broken forming hydrocarbons or H 2, and substituting the aluminium by alkoxy groups It is irrelevant whether other groups (for example higher alcohol residues (a higher alcohol being an alcohol having more than 6 carbon atoms) or halogen atoms) are also split off from the aluminium with the alcohol, because, like the alcohol, the resulting compounds contain acidic hydrogen atom which, during the backtitration with an organometallic compound, is detected in addition to that of the alcohol still present.

The unreacted alcohol and/or the acidic hydrogen atoms, e g derived from any Al-OR wherein R represents a higher alcohol residue, or A 1 -Hal bonds present in the substrate are subjected to back titration after decomposition The alkali metal compounds of polynuclear aromatic substances, for example naphthalene or anthracene, have proved to be suitable reagents They may be prepared by direct reaction of the alkali metal with the aromatic compound in a polar organic solvent, preferably an ether, for example, tetrahydrofurane dioxan or dimethoxyethane, at room temperature (compare H F Ebel, A Luttringhaus in Houben-Weyl, Methoden der Organischen Chemie 13/1 254 ( 1970)) The compounds resulting thereby are deep blue or green and lose their colour in a reaction with compounds having acidic hydrogen atoms, for example methanol In the titration, the end product can therefore easily be recognised, and an indicator does not have to be added The concentration of the organometallic compound should preferably be from 0 05 to 0 5 molar, especially from 0 1 to 0 2 molar As these compounds are sensitive to oxygen and water, they have to be handled under a protective gas, for example argon or nitrogen.

The invention will now be described, by way of example only, with reference to the accompanying drawing which shows an apparatus in which the process of the invention may be performed.

This apparatus comprises a schienk vessel 1, having a connecting tube 2 and a filling opening 3 The schlenk vessel 1 has a capacity of 1 litre, and the inlet opening 3 is provided with an NS 29 A 10 ml burette 4 is fused on to the top of the schlenk vessel 1 The outlet of the burette 4 is placed in a spacer piece S which has an inlet tube 5 a, and which is joined to a 250 ml titration flask 7 by means of a ground ball-andsocket joint 6 The titration flask has an inlet tube 8.

In operation, the apparatus provides both a reaction vessel for the titration and a vessel for preparing and storing the anthracenylsodium reagent A protective gas may be introduced through the inlet tube 5 a, and the inlet tube 8 may be used for passage of the 70 protective gas or for introduction of the solution to be titrated The contents of the schienk vessel 1 and the titration flask 7 may be stirred by a magnetic stirrer The titration is carried out by tipping the schienk vessel 1 75 to fill the burette 4 which is then placed in position over the titration flask 7.

The apparatus described corresponds to a large extent to an apparatus described in the literature (compare H Metzger, E Muller, in 80 Houben-Weyl, Methoden der Organischen Chemie, 1/2, 321, ( 1959), Diagram 72, page 373).

The following Example illustrates the invention 85 1 Purification of tetrahydrofuran {(THF) Apparatus: Distillation apparatus under protective gas; 4 litre round-bottomed flask; silver jacket column ( 80 cm) filled with Raschig rings; top of column for adjusting 90 the reflux ratio.

2.5 litre of THF were boiled for about 4 hours over sodiumpotassium alloy under reflux, then the THF was distilled under protective gas at a reflux ratio 1:1 After the 95 first distillate had been removed, the condenser was replaced by the schlenk vessel of the apparatus of Figure 1 About 1 litre of THF was then distilled.

2 Purification of anthracene 100 300 g of toluene and 39 g of anthracene were placed in a 500 ml Erlenmeyer flask equipped with a magnetic stirrer and heated to 100 C while stirring to dissolve the anthracene After the addition of 2 spatula tips of active charcoal 105 and repeated through mixing, filtration was carried out hot over a folded filter After cooling to room temperature, the precipitated crystals were suctioned off on a suction filter and washed with cold toluene The purified 110 anthracene was dried under vacuum in a dessicator and stirred over blue gel.

3 Preparation of anthracenyl-sodium solution In the apparatus shown in the Figure, 200 mmole (= 4 6 g) of finely chopped sodium were 115 added to the THF 100 mmoles (= 17 8 g) of anthracene were then added, the additions being made under a flow of protective gas The deep blue colour of the anthracenyl-sodium occurred immediately The formation of the 120 anthracenyl-sodium was effected while stirring at room temperature and was complete after a few hours (for example, overnight).

4 Analysis of titre To analyse the titre, 50 ml of a hydrocarbon 125 (for example n-hexane) were introduced as solvent into the apparatus described and this was titrated with the anthracenyl-sodium solution to decomposition, in order to destroy the impurities still present The titration was 130 1 574 225 effected under protective gas 50 1 l of methanol were then injected under protective gas and titration was carried out, while stirring, again until a sudden change in colour occurred The titre x was calculated according to the following equation:

1.235 V 1 x = titre in mmoles/ml V 1 = volume of the anthracenyl-sodium solution which was required to react with 50 #1 of methanol.

The value 1 235 indicates the number of millimoles which correspond to 50 pl of methanol.

Analysis of the concentration of the "active"aluminium in hydrocarbons The sample to be analysed was in a 1 litre vessel Under protective gas, 50 1 l of methanol were added to 100 ml of this sample.

(Methanol must always be present in excess).

The sample was shaken and then left to stand for 1 hour at room temperature A 3 (C 2 Hs)3 or at 60 C for Al-isoprenyl The decomposition was then complete After the decomposition, the volume of the solution was determined (at room temperature or at 60 C).

For the back titration of the methanol still present, 100 ml of the solution is removed again under protective gas, this sample was introduced into the heated titration flask cooled under protective gas and the unconsumed methanol was back titrated with the anthracenyl-sodium solution prepared in stage 3.

The end product of the titration was distinguished by the sudden change from deep blue to colourless or weakly yellow.

To calculate the concentration of the "active" aluminium the following variables must be known:

V = volume of the sample at room temperature or at 60 C in ml.

v = volume of the methanol added in pl.

V 2 = anthracenyl sodium solution consumed in the back titration for 100 ml of the sample, with the titre x in ml.

The concentration of the active aluminium at room temperature ( 25 C) was calculated according to the following equation:

lA 1 R 3 l = 10 ( 2 47 V f x V 2).

The factor f gives the ratio of the densities of the solvent used at 25 C and at 60 C When the decomposition is carried out at 25 C, the factor is 1.

This method enables the A 1-C and A 1-H bonds to be analysed in the concentration range of 10 mmoles/dm 3 within a limit of error generally of at most 10 % with a statistical reliability of 95 % This result was obtained for Al(C 2 H 5)3 and for aluminium sesquichloride, as the following values show:

Analysis of the Al-C-bonds in Esso-Varsol All values are calculated on A 1 R 3 or A 12 R 3 C 13.

Sample AI-C/mmole Al Et 3/mmole A 12 Et 3 CI 3/mmole 0.515 mmoles of Al Et 3 in 1 68 0 56 ml of Esso-Varsol 1 45 0 48 1.30 0 43 1.34 0 45 1.58 0 53 1.74 0 58 1.44 0 48 1.44 0 48 1.47 0 49 1.69 0 56 1.60 0 53 1.77 0 59 1.64 0 55 1.59 0 53 1.68 0 56 1.71 0 57 0.493 mmoles of A 12 Et 3 CI 3 0 66 0 44 in 100 ml of Esso-Varsol 0 78 0 52 0.77 0 52 0.68 0 45 1 574 225 Each sample was decomposed for 60 minutes with 100 tl of CH 30 H= 2 47 mmoles; the excess alcohol was subjected to back titration with Na-anthracenyl; Et = -C 2 H 5.

Claims (1)

1. WHAT WE CLAIM IS:

   1 A process for the quantitative analysis of aluminium/carbon and aluminium/hydrogen bonds in a sample comprising one or more hydrocarbons and containing at least one compound having an aluminium/carbon and/or aluminium/hydrogen bond, which comprises reacting the sample with an excess of an alcohol and back-titrating the unreacted alcohol and/or any compound, or compounds, formed during the reaction which contain acidic hydrogen atoms with a solution of a coloured organometallic compound, which compound is the reaction product of an alkali metal with a polynuclear aromatic hydrocarbon, wherein the coloured organometallic compound is decolourised by reaction with acidic hydrogen atoms.

   2 A process as claimed in claim 1, wherein the alcohol is an alkanol.

   3 A process as claimed in either claim 1 or 2, wherein the alcohol is a lower alcohol as hereinbefore defined.

   4 A process as claimed in any one of claims 1 to 3, wherein the polynuclear aromatic hydrocarbon is napthalene or anthracene.

   5 A process as claimed in any one of claims 1 to 3, wherein the coloured organometallic compound is anthracenylsodium.

   6 A process as claimed in any one of claims 1 to 5, wherein the substrate contains aluminium/carbon and/or aluminium/hydrogen bonds 35 in a concentration of less than 10 mmoles/dm 3.

   7 A process as claimed in any one of claims 1 to 6, wherein the substrate contains at least one compound having aluminium/halogen and/ or aluminium/alkoxy bonds 40 8 A process as claimed in any one of claims 1 to 7, wherein the concentration of the coloured organometallic compound is in the range of from 0 05 to 0 5 molar.

   9 A process as claimed in claim 8, wherein 45 the concentration of the coloured organometallic compound is in the range of from 0 1 to 0 2 molar A process as claimed in any one of claims 1 to 9, wherein the substrate comprises a reac 50 tion mixture from a process for the lowpressure polymerisation of a-olefins.

   11 A process as claimed in claim 1, carried out substantially as described herein with reference to the apparatus illustrated by the 55 accompanying drawing.

   12 A process as claimed in claim 1, carried out substantially as described in the Example herein.

   ABEL & IMRAY Chartered Patent Agents, Northumberland House, 303/306 High Holborn London WC 1 V 7 LH Agents for the Applicants Printed for Her Majesty's Stationery Office by MULTIPLEX techniques ltd, St Mary Cray, Kent 1980 Published at the Patent Office, 25 Southampton Buildings, London WC 2 l AY, from which copies may be obtained.